Apparatus and method for transmitting and receiving control information in a mobile communication system

ABSTRACT

Disclosed is an apparatus and method for transmitting and receiving control information for a packet data channel in a mobile communication system supporting a high-speed packet data service and a circuit voice service. A base station generates control information indicating an encoder packet size, a code rate and the number of Walsh codes used for transmission of packet data to a mobile station, and transmits the generated control information over a packet data control channel. The mobile station receives the control information over the packet data control channel while receiving the packet data over the packet data channel, and decodes the received packet data according to a modulation order determined based on the received control information.

PRIORITY

[0001] This application claims priority to an application entitled“Apparatus and Method for Transmitting and Receiving Control Informationin a Mobile Communication System” filed in the Korean IndustrialProperty Office on Nov. 30, 2001 and assigned Serial No. 2001-75309, thecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a mobile communicationsystem supporting a packet data service, and in particular, to anapparatus and method for transmitting and receiving control informationrelated to a packet data channel (PDCH) for carrying packet data.

[0004] 2. Description of the Related Art

[0005] A typical mobile communication system provides only a voiceservice to a mobile station (MS). However, with the development of thecommunication technology and at the request of users, researches havebeen carried out on a mobile communication system for supporting notonly the voice service but also a data service for image communicationand various Internet-related capabilities. A base station (BS)supporting both the voice and data services commonly classifies channelsinto circuit-based radio channels for the voice service and packet-basedradio channels for the data service, and assigns the remaining radioresources except the radio resources used for the packet channels topacket channels. Here, the “radio resources” refer to transmissionpower, the number of Walsh codes, and a transmission period.

[0006] A CDMA2000 (Code Division Multiple Access 2000) 1xEV-DV(Evolution in Data and Voice) system, proposed to support both the voiceservice and high-speed packet data service, employs time divisionmultiplexing (TDM) in order to transmit packet data to a plurality ofusers over a limited number of packet channels. A base stationsupporting the time division multiplexing assigns the entire power andWalsh codes available for packet data transmission to one mobile stationfor a particular time period. The base station selects mobile stations,to which it will assign radio resources every time period, byscheduling.

[0007] All mobile stations desiring to receive a data service from thebase station must periodically report quality information of the radiochannels to the base station. The base station then selects an optimalmobile station every time period, taking into account the radio channelquality information received from the mobile stations and an amount ofaccumulated data to be transmitted to the mobile stations so that theselected mobile station can maximize its data throughput whilemaintaining a data rate.

[0008] In the 1xEV-DV system, the number of Walsh codes available forpacket data service is a maximum of 28, and the minimum time unit fortransmitting packet data is 1.25 ms, which is called a “time slot (TS).”Actually, a time period for transmitting unit packet data becomes one of1 TS, 2 TSs, 4 TSs, and 8 TSs, and data with a predetermined size istransmitted for this time period. The data with a predetermined size iscalled “encoder packet,” since it is encoded at once by an encoder in abase station transmitter.

[0009] A size of the encoder packet that can be transmitted for a timeperiod is defined as 384, 768, 1,536, 2,340, 3,072 and 3,840 bits. Theencoder packet undergoes encoding, interleaving and modulation by a basestation transmitter, and then spread by at least one Walsh code beforebeing transmitted over a packet data channel (PDCH). Here, a data rateis determined according to the encoder packet size and transmission timeperiod.

[0010] A code rate and a modulation order (or modulation technique) usedby a base station to transmit packet data are determined according tothe encoder packet size and the number of Walsh codes, in order toobtain optimal data throughput. Information on the encoder packet sizeand the number of Walsh codes (hereinafter, referred to as “controlinformation”) is transmitted to a mobile station over a separate packetdata control channel different from the packet data channel. The mobilestation then determines a modulation order and a code rate used fortransmission of the packet data channel based on the controlinformation, and receives packet data over the packet data channel.

[0011] Table 1 illustrates a frame format of control informationtransmitted over a packet data control channel (PDCCH). TABLE 1 FieldLength in Bits MAC ID 8 ARQ Channel ID 2 Encoder Packet Size 3 SubpacketID 2 Total 15

[0012] Describing information fields shown in Table 1, a MAC ID (MediumAccess Control Identifier) field, indicating a unique identifierassigned to a mobile station desiring to receive a packet data service,is used to identify a mobile station that intends to transmit controlinformation. An ARQ (Automatic Repeat Request) Channel ID field is usedto identify a maximum of 4 data packets that can be simultaneouslytransmitted to one mobile station. An Encoder Packet Size field,indicating a size of transmission packet data, is assigned 3 bits toidentify the 6 predefined sizes of 384, 768, 1,536, 2,340, 3,072, and3,840 bits. A Subpacket ID field is used to identify a format of codedsymbols to be used during initial transmission and retransmission.

[0013] The number of Walsh codes is represented using all fields exceptthe MAC ID fields at predetermined periods or each time the number ofWalsh codes is changed, and the MAC ID is set to ‘000000’. If MAC ID isset to ‘000000’, all mobile stations acquire information on the numberof Walsh codes. In addition, a transmission time period (or the numberof time slots) of packet data is equal to the transmission time periodof a control information transmitted on a packet data control channel.

[0014]FIG. 1 illustrates a structure of a base station transmitter fortransmitting control information over a packet data control channel(PDCCH) according to the prior art. Referring to FIG. 1, an 8-bit errorcorrection code is added by an error correction code adder 110 to the15-bit control information (MAC ID, ARQ Channel ID, Encoder Packet Sizeand Subpacket ID) illustrated in Table 1, and then 8 tail bits are addedto the error correction code-added control information by a tail bitadder 120, for convergence into a specified state during decoding. Aconvolutional encoder 130 encodes 29 output bits from the tail bit adder120 at a code rate R determined based on the control information, andoutputs coded symbols. For example, if the control information istransmitted over 1 TS (N=1), the code rate becomes R=½. If the controlinformation is transmitted over 2 TSs (N=2) or 4 TSs (N=4), the coderate becomes R=¼.

[0015] The coded symbols output from the convolutional encoder 130 areproperly repeated by a symbol repeater 140 according to the transmissiontime period of the control information. That is, if the controlinformation is transmitted over 1 TS or 2 TSs (N=1 or 2), the inputcoded symbols are not repeated, and if the control information istransmitted over 4 TSs (N=4), the input coded symbols are repeated once.A symbol puncturer 150 punctures some of the repeated coded symbolsaccording to a predetermined puncturing pattern, and outputs theremaining non-punctured symbols.

[0016] An interleaver 160 sets a size of its interleaving memoryaccording to the number of symbols received from the symbol puncturer150, and interleaves the received symbols using the interleaving memory.A modulator 170 modulates the interleaved symbols according to apredetermined modulation order (e.g., QPSK (Quadrature Phase ShiftKeying)) and outputs modulation (or modulated) symbols. A Walsh spreader180 spreads the modulation symbols output from the modulator 170 with a64-chip length Walsh code assigned to the packet data control channel.The Walsh code assigned to the packet data control channel isdistinguishable from Walsh codes assigned to packet data channels.Although it is not shown, the output of the Walsh spreader 180, togetherwith an output of a packet data channel transmitter, are converted intoan RF (Radio Frequency) band signal through spreading by a PN(Pseudo-random Noise) code and baseband filtering, and then transmittedthrough an antenna.

[0017] A mobile station can acquire information on an encoder packetsize, a transmission time period and the number of Walsh codes relatedto a packet data channel, from control information received over apacket data control channel, determine a code rate and a modulationorder used by a base station for transmission of the packet datachannel, based on the acquired information and can decode a receiveddata on packet data channel.

[0018] In such a mobile communication system, a base station uses amapping table representing a mapping relationship between a code rateand a modulation order based on the number of Walsh codes and the numberof transmission time slots for an encoder packet size, in order toprovide information on a code rate and a modulation order to a mobilestation. FIG. 2 illustrates an portion of a mapping table for a3,840-bit encoder packet size. In a Modulation Order column of themapping table, “2” represents QPSK (Quadrature Phase Shift Keying), “3”represents 8-PSK (8-ary Phase Shirt Keying), and “4” represents 16-QAM(16-ary Quadrature Amplitude Modulator).

[0019] Referring to FIG. 2, when a base station transmits a 3,840-bitsize encoder packet (or coded packet) according to a modulation order of16-QAM and an effective code rate of 0.625 and the base station uses 4Walsh codes during an 8-TS transmission time period. In this case, thebase station transmits control information representing the 3,840-bitencoder packet, the 4 Walsh codes and the 8-TS transmission time periodover a packet data control channel, by consulting the previously storedmapping table of FIG. 2. A mobile station then receives the controlinformation over the packet data control channel, and determines thatthe modulation order of 16-QAM and the effective code rate of 0.625 wereused for the packet data channel, by consulting the mapping table ofFIG. 2 corresponding to the 3,840-bit size among mapping tablespreviously stored therein.

[0020] As described above, in the prior art, the base station and themobile station require a plurality of mapping tables according to theencoder packet sizes. That is, the base station and the mobile stationmust previously store mapping tables of FIG. 2 for the individualencoder packet sizes, before they start data communication. In order tostore the mapping tables, larger memory capacity is required. As aresult, the base station and the mobile station must increase theirrequired memory capacity. The increase in memory capacity may be aninsignificant matter in the base station, which has no limitation on thememory capacity. However, in the case of the mobile station, theincrease in the required memory capacity is disadvantageous whenminimization and reduction in power consumption and cost of the mobilestation is desired.

[0021] In addition, when a mobile station sends a retransmission requestfor received packet data due to an error that occurred in the receivedpacket data, a base station may select for retransmission a modulationorder and a code rate different from those used at initial transmissionin order to increase reception efficiency of the mobile station.However, since the mapping table defines possible modulation order andcode rate according to the number of Walsh codes and a transmission timeperiod, the base station has a limitation in adaptively selecting amodulation order and a code rate according to a radio channel condition.Thus, to support more various combinations of the modulation orders andcode rates, it is necessary to increase a size of the mapping table.However, the increase in size of the mapping table causes an increase innecessary memory capacity of the base station and the mobile station.

SUMMARY OF THE INVENTION

[0022] It is, therefore, an object of the present invention to providean apparatus and method for transmitting information on a modulationorder used by a base station for transmission of packet data.

[0023] It is another object of the present invention to provide anapparatus and method for receiving, by a mobile station, information ona modulation order used by a base station for transmission of packetdata.

[0024] It is further another object of the present invention to providean apparatus and method for determining by a mobile station a modulationorder used by a base station for transmission of packet data, withoutusing a separate mapping table.

[0025] To achieve the above and other objects, the present inventionprovides a method for transmitting control information for a packet datachannel in a transmitter for a mobile communication system, whichencodes an encoder packet at a predetermined code rate, modulates thecoded packet according to a predetermined modulation order, spreads themodulated packet with at least one Walsh code and transmits the spreadpacket over the packet data channel. The method in one embodimentcomprises generating control information indicating parameters used fortransmission of the spread packet over the packet data channel; andinserting at least one bit indicating a modulation order used fortransmission the spread packet among a plurality of available modulationorders into one information field in the control information, andtransmitting the control information.

[0026] To achieve the above and other objects, the present inventionprovides a method for receiving control information for a packet datachannel by a receiver in a mobile communication system which encodes anencoder packet at a predetermined code rate, modulates the coded packetaccording to a predetermined modulation order, spreads the modulatedpacket with at least one Walsh code and transmits the spread packet tothe receiver over the packet data channel. The method comprisesreceiving control information indicating parameters used fortransmission of the spread packet over the packet data channel, over apacket data control channel physically distinguishable from the packetdata channel; and extracting, from an information field in the receivedcontrol information, at least one bit indicating a modulation order usedfor transmission of the spread packet among a plurality of availablemodulation orders.

[0027] To achieve the above and other objects, the present inventionprovides an apparatus for transmitting control information for a packetdata channel in a transmitter for a mobile communication system, whichencodes an encoder packet at a predetermined code rate, modulates thecoded packet according to a predetermined modulation order, spreads themodulated packet with at least one Walsh code and transmits the spreadpacket over the packet data channel. The apparatus in one embodimentcomprises a control information generator for generating controlinformation indicating parameters used for transmission of the spreadpacket over the packet data channel, and inserting at least one bitindicating a modulation order used for transmission of the spread packetamong a plurality of available modulation orders into one informationfield in the control information; and a control information transmitterfor transmitting the control information over a packet data controlchannel physically distinguishable from the packet data channel.

[0028] To achieve the above and other objects, the present inventionprovides an apparatus for receiving control information for a packetdata channel by a receiver in a mobile communication system whichencodes an encoder packet at a predetermined code rate, modulates thecoded packet according to a predetermined modulation order, spreads themodulated packet with at least one Walsh code and transmits the spreadpacket to the receiver over the packet data channel. The apparatus inone embodiment comprises a control information receiver for receivingcontrol information indicating parameters used for transmission of thespread packet, over a packet data control channel physicallydistinguishable from the packet data channel; and an extractor forextracting, from an information field in the received controlinformation, at least one bit indicating a modulation order used fortransmission of the spread packet data among a plurality of availablemodulation orders.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0030]FIG. 1 illustrates a structure of a transmitter for transmittingcontrol information over a packet data control channel according to theprior art;

[0031]FIG. 2 illustrates an example of a mapping table for a 3,840-bitencoder packet size;

[0032]FIG. 3 is a flowchart illustrating a procedure for transmittingpacket data and control information by a base station transmitteraccording to an embodiment of the present invention;

[0033]FIG. 4 is a flowchart illustrating a procedure for receivingpacket data and control information by a mobile station receiveraccording to an embodiment of the present invention;

[0034]FIG. 5 illustrates the number of coded symbols transmittedaccording to a modulation order and a transmission time period for apacket data channel;

[0035]FIG. 6 illustrates a structure of a transmitter for transmittingcontrol information in a base station according to an embodiment of thepresent invention; and

[0036]FIG. 7 illustrates a structure of a receiver for receiving controlinformation in a mobile station according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0037] A preferred embodiment of the present invention will be describedherein below with reference to the accompanying drawings. In thefollowing description, well-known functions or constructions are notdescribed in detail since they would obscure the invention inunnecessary detail.

[0038] In the following description, the present invention provides amethod for determining by a base station an encoder packet size, thenumber of Walsh codes and a modulation order over a packet data channel,and transmitting the determined control information over a packet datacontrol channel formed separately from the packet data channel during atransmission time period. The transmission time period is equal to atransmission period of packet data.

[0039] Herein, a detailed description of the present invention will bemade with reference to a CDMA2000 1xEV-DV (Evolution in Data and Voice)system, a synchronous CDMA communication system. However, it will beunderstood by those skilled in the art that the novel technique fortransmitting control information for a packet data channel can beapplied to other mobile communication systems having the similartechnical background and channel formats without departing from thespirit and scope of the invention.

[0040] In addition, although the present invention will be describedwith reference to a case where time division multiplexing (TDM) is usedfor a packet data channel, the invention can be applied in the samemanner to a TDM/CDM (Time Division Multiplexing/Code DivisionMultiplexing) system in which mobile stations share assigned timeperiods with Walsh codes, and a TDM/TDM (Time Division Multiplexing/TimeDivision Multiplexing) system in which mobile stations divide assignedtime periods more finely.

[0041] First, a description will be made of packet data transmission bya base station. The base station determines a modulation order and acode rate according to transmission parameters to be used fortransmission of packet data, i.e., an encoder packet size, the number ofWalsh codes and the number of time slots, segments a packet data streamfor a mobile station in a unit of the encoder packet size, encodes thesegmented packet data at the code rate, modulates the coded packet dataaccording to the modulation order, spreads the modulated packet datawith Walsh codes, and then transmits the spread packet data over apacket data channel.

[0042] Here, the base station inserts information about the modulationorder into control information including information about the encoderpacket size at least, and transmits the control information over apacket data control channel. Table 2 illustrates a frame format ofcontrol information transmitted over a packet data control channelaccording to an embodiment of the present invention. TABLE 2 FieldLength in Bits MAC ID 8 ARQ Channel ID 2 Encoder Packet Size 3 SubpacketID 2 Modulation Order 2 Total 17

[0043] It is noted that compared with Table 1, Table 2 further includesa Modulation Order field indicating a modulator order. Since modulationorders defined by the CDMA2000 1xEV-DV include QPSK (Quadrature PhaseShift Keying), 8-PSK (8-ary Phase Shift Keying) and 16-QAM (16-aryQuadrature Amplitude Modulation), the Modulation Order field is assigned2 bits in order to identify these 3 types of the modulation orders. Eventhough 64-QAM (64-ary Quadrature Amplitude Modulation) is additionallyused, the 2 bits assigned to the Modulation Order field are sufficientto identify the modulation orders. However, if only two types ofmodulation orders are used, the Modulation Order field may be assigned 1bit.

[0044] The number x of Walsh codes assigned to a packet data channel isrepresented using all fields except the MAC ID fields at predeterminedperiods or each time the period value is changed, and the MAC ID is setto ‘000000’. If MAC ID is set to ‘000000’, all mobile stations acquireinformation on the number of Walsh codes through a packet data controlchannel. In addition, a transmission time period (or the number of timeslots) of packet data is previously agreed between a base station and amobile station so that the number of Walsh codes assigned it can bedetermined based on a transmission time period and an initial codingstate of control information

[0045]FIG. 3 is a flowchart illustrating a procedure for transmittingpacket data and control information by a forward transmitter in a basestation according to an embodiment of the present invention. Referringto FIG. 3, in step 210, the base station acquires forward radio channelquality information, specifically a measured carrier-to-interferenceratio (C/I) of a forward pilot channel from each mobile station in dataservice. In step 220, the base station calculates the number of Walshcodes and transmission power, to be assigned for a packet data service.Though not separately illustrated, control information on the calculatednumber of Walsh codes is transmitted to every mobile station over apacket data control channel by periods or each time the number of Walshcodes is changed.

[0046] In step 230, based on the acquired radio channel qualityinformation and an amount of data to be transmitted to the mobilestations, a packet transmission scheduler of the base station selects amobile station to which it will assign a packet data channel, anddetermines an encoder packet size. Preferably, the scheduler firstselects a mobile station having a better radio channel quality orgreater amount of transmission data in order to increase data throughputof the system.

[0047] In step 240, based on forward radio channel quality informationof the selected mobile station and the transmission power allocated forthe packet data service, the base station determines the number of timeslots, a modulation order and a code rate to be used for transmission ofpacket data to the selected mobile station, and generates controlinformation indicating the determined values. Here, the base stationdetermines a code rate and a modulation order in various ways,regardless of the encoder packet size, the transmission time period andthe number of Walsh codes. Preferably, the code rate and the modulatororder are determined according to radio channel environments and datathroughput of the system.

[0048] In step 250, a packet data channel transmitter of the basestation encodes an encoder packet with a predetermined size at thedetermined code rate, modulates the coded encoder packet by a knownmodulation technique having the determined modulation order, and spreadsthe modulated packet using the determined number of Walsh codes, beforetransmission. Further, in step 260, a packet data control channeltransmitter of the base station transmits the control information aboutthe encoder packet size, the number of time slots and the modulationorder, through encoding, modulation and spreading. As described above,the control information about the number of Walsh codes is broadcast toall mobile stations regardless of presence of the transmission data.

[0049]FIG. 4 is a flowchart illustrating a procedure for receivingpacket data and control information by a forward receiver in a mobilestation according to an embodiment of the present invention. Referringto FIG. 4, in step 310, a packet data control channel receiver of themobile station acquires information about the encoder packet size, thenumber of time slots and the modulation order related to a packet datachannel, through a packet data control channel. Here, the packet datacontrol channel receiver can determine the encoder packet size and themodulator order from control information acquired by decoding datareceived over the packet data control channel, and can determine thenumber of time slots in the process of decoding the packet data controlchannel. It will be assumed herein that the mobile station previouslyacquires control information on the number of Walsh codes assigned tothe packet data channel. The control information further includes MAC IDindicating a mobile station that desires to transmit packet data to thebase station. The mobile station enables in step 320 its packet datachannel receiver only when MAC ID included in the control information isidentical to its own MAC ID.

[0050] In step 320, the packet data channel receiver receives packetdata in the form of a Walsh symbol by despreading data received over apacket data channel every time slot with as many Walsh codes as thenumber of the assigned Walsh codes. In step 330, based on the controlinformation, the packet data channel receiver demodulates Walsh symbolsreceived for as many time periods as the number of time slots by ademodulation technique corresponding to the modulation technique used bythe base station. In step 340, the packet data channel receiverdeinterleaves and decodes the demodulated symbols. In step 350, thepacket data channel receiver checks the decoded packet data to determinewhether the packet data was correctly received. If the received data hasan error, the packet data channel receiver transmits a retransmissionrequest for the received packet data to the base station.

[0051] When a mobile station fails to correctly receive packet datainitially transmitted by a base station, the mobile station stores theinitially received data instead of discarding it, and then combines theinitially received data with re-received data during decoding. In thiscase, for retransmission, the base station can successfully transmitpacket data without using as many resources as those used at initialtransmission.

[0052] The number of coded symbols transmitted by a base station everytransmission time period is determined according to a modulation orderand a length of a transmission time period used by the base station.FIG. 5 illustrates the number of coded symbols transmitted according toa modulation order and a transmission time period in the case where apacket data channel uses a chip rate of 1.2288 Mcps (Mega chips persecond) and each time slot has a 1.25 ms length. In FIG. 5, Nw,representing the number of Walsh codes, is a maximum of 28 in the1xEV-DV system. For example, if the coded packets are modulated by QPSKmodulation for 1 TS using 28 Walsh codes, then 2,688 (=96×28) codedsymbols are actually transmitted. However, if 16-QAM modulation is used,then 5,376 (=192×28) coded symbols are transmitted.

[0053] For FIG. 5, a transmission procedure of the packet data channeltransmitter will be described inversely. In order to support thestandard chip rate of 1.2288 Mcps, a Walsh spreader in the packet datachannel transmitter must generate 1,536 chips for a 1.25 ms time period(1 TS). Since a packet data channel uses a 32-chip length Walsh code,the number of modulation symbols to be generated by a modulator in thepacket data channel transmitter for 1.25 ms (1 TS) is 48 (=1,536chips/32 chips). Here, the number of coded symbols mapped to eachmodulation symbol is 2 for QPSK modulation, 3 for 8-PSK modulation, and4 for 16-QAM modulation. Therefore, the number of coded symbols neededto generate 48 modulation symbols becomes 96 (=48×2) for QPSKmodulation, 144 (=48×3) for 8-PSK modulation, and 192 (48×4) for 16-QAMmodulation.

[0054] As the number of time slots and Walsh codes increases, the numberof coded symbols being transmitted also increases. Therefore, the packetdata channel transmitter repeats and/or punctures coded symbols outputfrom an encoder, in order to match the number of coded symbols outputfrom the encoder to the number of coded symbols being transmitted.

[0055]FIG. 5 illustrates the number of coded symbols actuallytransmitted according to only the modulation order, the number of timeslots and the number of Walsh codes, and in this case, a base stationand a mobile station do not store the illustrated mapping table. Thatis, the mobile station calculates the number of coded symbols beingactually transmitted/received, based on the modulation order, the numberof time slots and the number of Walsh codes, acquired from the controlinformation.

[0056]FIG. 6 illustrates a structure of a packet data control channeltransmitter for transmitting control information in a base stationaccording to an embodiment of the present invention. As illustrated, thepacket data control channel transmitter includes an error correctioncode adder 410, a tail bit adder 420, a convolutional encoder 430, asymbol repeater 440, a symbol puncturer 450, an interleaver 460, amodulator 470, a Walsh spreader 480, a control information generator400, and a transmission controller 490.

[0057] Here, the error correction code adder 410, the tail bit adder420, the convolutional encoder 430, the symbol repeater 440, the symbolpuncturer 450, the interleaver 460, the modulator 470, and the Walshspreader 480 constitute a control information transmitter for actuallytransmitting control information generated by the control informationgenerator 400, and the transmission controller 490 controls transmissionblocks of the control information transmitter.

[0058] Though not illustrated, a packet data channel transmitter of thebase station selects a mobile station to which it will transmit packetdata, based on forward radio channel quality information acquired fromall mobile stations in packet data service, and determines an encoderpacket size, a code rate, a modulation order, and a transmission timeperiod (or the number of time slots) to be used for transmission ofpacket data to the selected mobile station. It is assumed thatinformation on the number of Walsh codes to be used for transmission ofthe packet data is previously broadcast to all mobile stations.

[0059] Meanwhile, the control information generator 400 generatescontrol information used for transmission of packet data to the selectedmobile station. The control information, as described in conjunctionwith Table 2, is 17-bit frame information comprised of MAC ID field, ARQChannel ID field, Encoder Packet Size field, Subpacket ID field, andModulation Order field. The transmission controller 490 determinesparameters to be used in the transmission blocks for each of the caseswhere the packet data service is applied to TDM, TDM/TDM and TDM/CDM.Herein, the embodiment of the present invention will be described withreference to a case where the packet data service is applied to TDM.

[0060] An 8-bit error correction code is added by the error correctioncode adder 410 to the 17-bit control information generated by thecontrol information generator 400, and then, 8 tail bits are added tothe error correction code-added control information by the tail bitadder 420, for convergence into a specified state during decoding. Theconvolutional encoder 430 encodes 33 output bits from the tail bit adder420 at a code rate R determined based on a transmission time period ofthe control information, and outputs coded symbols. For example, if thecontrol information is transmitted over 1 TS (N=1), the code ratebecomes R=½. If the control information is transmitted over 2 TSs (N=2)or 4 TSs (N=4), the code rate becomes R=¼.

[0061] The coded symbols output from the convolutional encoder 430 areproperly repeated by the symbol repeater 440 according to thetransmission time period of the control information. That is, if thecontrol information is transmitted over 1 TS or 2 TSs (N=1 or 2), theinput coded symbols are not repeated, and if the control information istransmitted over 4 TSs (N=4), the input coded symbols are repeated once.The symbol puncturer 450 punctures some of the repeated coded symbolsaccording to a predetermined puncturing pattern, and outputs theremaining non-punctured symbols.

[0062] The interleaver 460 sets a size of its interleaving memoryaccording to the number of symbols received from the symbol puncturer450, and interleaves the received symbols using the interleaving memory.The modulator 470 modulates the interleaved symbols according to apredetermined modulation order (e.g., QPSK) and outputs modulation (ormodulated) symbols. The Walsh spreader 480 spreads the modulationsymbols output from the modulator 470 with a 64-chip length Walsh codeassigned to the packet data control channel. The Walsh code assigned tothe packet data control channel is distinguishable from Walsh codesassigned to packet data channels. The output of the Walsh spreader 480,together with an output of the packet data channel transmitter, areconverted into an RF (Radio Frequency) band signal through spreading bya PN (Pseudo-random Noise) code and baseband filtering, and thentransmitted through an antenna.

[0063] The output of the packet data channel transmitter is equal to asignal obtained by encoding as much packet data as the determinedencoder packet size at the determined code rate, modulating the codedpacket data by the determined modulation technique, and spreading themodulated packet data with as many Walsh codes as the determined numberof Walsh codes.

[0064]FIG. 7 illustrates a structure of a packet data control channelreceiver for receiving control information in a mobile station accordingto an embodiment of the present invention. As illustrated, the packetdata control channel receiver includes a Walsh despreader 510, amultipath symbol accumulator 520, a deinterleaver 530, a depuncturer540, a subsequent symbol accumulator 550, a decoder 560, an errorcorrection code detector 570, and a reception controller 580.

[0065] Reception of the control information is performed in reverseprocess to transmitting the control information. The receptioncontroller 580 determines parameters to be applied to reception blocksfor each of the cases where the packet data service is applied to TDM,TDM/TDM and TDM/CDM. Herein, the embodiment of the present inventionwill be described with reference to a case where the packet data serviceis applied to TDM.

[0066] Referring to FIG. 7, the Walsh despreader 510 despreads datareceived from a base station with a Walsh code assigned to the packetdata control channel. Though not illustrated, the Walsh despreader 510performs Walsh despreading on each of multiple reception paths. Themultipath symbol accumulator 520 accumulates as many symbols, despreadby the Walsh despreader 510, as the number of multiple reception paths.

[0067] The accumulated symbols are deinterleaved by the deinterleaver530 according to a deinterleaving rule corresponding to the interleavingrule used in the base station. The depuncturer 540 inserts apredetermined number of ‘0’ symbols between the deinterleaved symbolsaccording to a depuncturing pattern corresponding to the puncturingpattern used in the base station. The symbols output from thedepuncturer 540 undergo accumulation through the subsequent symbolaccumulator 550. The accumulation corresponds to the symbol repetitionperformed in the base station. That is, the subsequent symbolaccumulator 550 accumulates input symbols once, only when a transmissiontime period of the control information is 4 TSs (N=4).

[0068] The symbols accumulated by the subsequent symbol accumulator 550are decoded by the decoder 560 at a predetermined code rate R. The coderate becomes R=½ for N=1, and R=¼ for N=2 or 4. The error correctioncode detector 570 checks whether the decoded information bits have anerror. If the decoded information bits have no error, the errorcorrection code detector 570 judges that the decoded information bitsare control information transmitted by the base station.

[0069] Though not illustrated, the mobile station checks whether MAC IDextracted from the control information is identical to its own MAC ID,and enables the packet data channel receiver, if the extracted MAC ID isidentical to its own MAC ID. The packet data channel receiver extractsinformation on transmission time period (or the number of time slots),modulation order, code rate and encoder packet size from the controlinformation, and performs Walsh despreading, demodulation and decodingon data received over a packet data channel based on the extractedinformation. Here, information on the number of Walsh codes needed todespread the received data is previously broadcast from the basestation.

[0070] Referring to above, the number of coded symbols transmitted by abase station every transmission time period is determined according to amodulation order and a length of a transmission time period used by thebase station. The number of coded symbols determinates the code rate andthe repetition number and the puncture pattern of the coded symbols. Inthe present invention, the base station transmits a modulation of apacket data channel over a packet data control channel. A mobile stationdecodes the information received the packet data control channel andacquires the number of coded symbols transmitted over the packet datachannel. Then, the mobile station can decode the packet data channelusing the number of coded symbols. The transmission time period of thepacket data channel is equal to the transmission time period of thepacket data control channel. The mobile station can acquire thetransmission time period of the packet data control channel using ablind rate detection.

[0071] As described above, the base station and the mobile stationaccording to the present invention do not require memories for storingmapping tables for mapping modulation orders and code rates according tothe encoder packet size and the number of Walsh codes for a packet datachannel. Therefore, the present invention is advantageous in reducingsize, power consumption and cost of the mobile station. In addition, thepresent invention enables the base station to select a modulation orderregardless of a combination of the encoder packet size, the number ofWalsh codes and the transmission time period, so the base station has nolimitation in determining a modulation order and a code rate for initialtransmission and retransmission according to a radio channelenvironment.

[0072] While the invention has been shown and described with referenceto a certain preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method for transmitting control information fora packet data channel in a transmitter for a mobile communication systemduring a transmission period equal to a transmission period of a packetdata, which encodes an encoder packet at a predetermined code rate,modulates the coded packet according to a predetermined modulationorder, spreads the modulated packet with at least one Walsh code andtransmits the spread packet over the packet data channel, the methodcomprising: generating control information indicating parameters usedfor transmission of the spread packet over the packet data channel; andinserting at least one bit indicating a modulation order used fortransmission of the spread packet among a plurality of availablemodulation orders into one information field in the control information,and transmitting the control information.
 2. The method of claim 1,wherein the control information is transmitted over a packet datacontrol channel physically distinguishable from the packet data channel.3. The method of claim 1, wherein the modulation orders include at leasttwo of QPSK (Quadrature Phase Shift Keying), 8-PSK (8-ary Phase ShiftKeying), 16-QAM (16-ary Quadrature Amplitude Modulation) and 64-QAM(64-ary Quadrature Amplitude Modulation).
 4. The method of claim 1,wherein the control information includes information about an encoderpacket size, a code rate and the number of Walsh codes used for thepacket data channel.
 5. A method for receiving control information overa packet data channel during a time period by a receiver in a mobilecommunication system which encodes an encoder packet at a predeterminedcode rate, modulates the coded packet according to a predeterminedmodulation order, spreads the modulated packet with at least one Walshcode and transmits the spread packet to the receiver over the packetdata channel, the method comprising: receiving and decoding a controlinformation over a packet data control channel physicallydistinguishable from the packet data channel, the control informationindicating parameters used for transmission of the spread packet overthe packet data channel; and extracting from an information field in thedecoded control information, at least one bit indicating a modulationorder used for transmission of the spread packet among a plurality ofavailable modulation orders.
 6. The method of claim 5, wherein themodulation orders include at least two of QPSK (Quadrature Phase ShiftKeying), 8-PSK (8-ary Phase Shift Keying), 16-QAM (16-ary QuadratureAmplitude Modulation) and 64-QAM (64-ary Quadrature AmplitudeModulation).
 7. An apparatus for transmitting control information for apacket data channel in a transmitter for a mobile communication systemduring a transmission period equal to a transmission period of a packetdata, which encodes an encoder packet at a predetermined code rate,modulates the coded packet according to a predetermined modulationorder, spreads the modulated packet with at least one Walsh code andtransmits the spread packet over the packet data channel, the apparatuscomprising: a control information generator for generating controlinformation indicating parameters used for transmission of the spreadpacket over the packet data channel, and inserting at least one bitindicating a modulation order used for transmission of the spread packetamong a plurality of available modulation orders into one informationfield in the control information; and a control information transmitterfor transmitting the control information over a packet data controlchannel physically distinguishable from the packet data channel.
 8. Theapparatus of claim 7, wherein the modulation orders include at least twoof QPSK (Quadrature Phase Shift Keying), 8-PSK (8-ary Phase ShiftKeying), 16-QAM (16-ary Quadrature Amplitude Modulation) and 64-QAM(64-ary Quadrature Amplitude Modulation).
 9. The apparatus of claim 7,wherein the control information includes information about an encoderpacket size, a code rate and the number of Walsh codes used for thepacket data channel.
 10. An apparatus for receiving control informationover a packet data channel during a time period by a receiver in amobile communication system which encodes an encoder packet at apredetermined code rate, modulates the coded packet according to apredetermined modulation order, spreads the modulated packet with atleast one Walsh code and transmits the spread packet to the receiverover the packet data channel, the apparatus comprising: a controlinformation receiver for receiving and decoding a control informationover a packet data control channel physically distinguishable from thepacket data channel, the control information indicating parameters usedfor transmission of the spread packet; and an extractor for extractingfrom an information field in the decoded control information, at leastone bit indicating a modulation order used for transmission of thespread packet data among a plurality of available modulation orders. 11.The apparatus of claim 10, wherein the modulation orders include atleast two of QPSK (Quadrature Phase Shift Keying), 8-PSK (8-ary PhaseShift Keying), 16-QAM (16-ary Quadrature Amplitude Modulation) and64-QAM (64-ary Quadrature Amplitude Modulation).
 12. A method forreceiving control information for a packet data channel by a receiverover a packet data control channel in a mobile communication system,wherein a transmission time period of the packet data channel is equalto a transmission time period of the packet data control channel, themethod comprising: acquiring a length of the transmission time period ofthe packet data control channel; extracting a modulation order, thenumber of the Walsh codes and the size of a encoder packet from acontrol information received over the packet data control channel duringthe acquired transmission time period; determining the number of codedsymbols received the packet data channel according to the acquiredtransmission time period and the modulation order; and decoding thepacket data channel using to the number of coded symbols.
 13. The methodof claim 12, wherein the number of coded symbols determines a code rate,the repetition number and a puncture pattern of the coded symbolsreceived over the packet data channel.